1. Introduction Recent decades have seen dramatic progress in work on animal communication and its evolution, on both empirical and theoretical fronts. Dorothy Cheney and Robert Seyfarth have long been leaders in this research, especially on the empirical side, with their extraordinarily rich studies of communication and social life in vervet monkeys (1990) and baboons (2007). A range of theoretical models of communication, developed in different fields, have also begun to cohere in recent years. These models illuminate different facets of the central phenomenon: the coevolution of two kinds of behavior seen in sign use. On one side are behaviors of sign production; on the other side are behaviors of sign interpretation. Communication is comprised of the ways these behaviors fit (or fail to fit) together. When a communication system has become established, the sounds, scents, or other marks that an animal makes have been conditioned, through selection, by the patterns of reception and interpretation waiting downstream. The converse is also true: the evolution of patterns of interpretation is an ongoing response to features of sign production. Production and interpretation coevolve. ...